Circuits and apparatus for delivering a constant-current pulse with stability compensation into low impedance pyrotechnic loads

Abstract

Circuits and apparatus for delivering a constant-current pulse with stability compensation into low impedance pyrotechnic loads are disclosed. One apparatus includes a power switch circuit including a high side connectable to an external device and for outputting current to the external device, a current sense circuit connected to the power switch circuit and for monitoring and limiting an amount of the current being output by the power switch circuit, a compensation circuit connected between the current sense circuit and the high side of the power switch circuit. The compensation circuit includes circuitry to provide gain and phase margin over a frequency range that provides stability in the current being output by the power switch circuit over a range of temperatures, input voltages, load impedances, and harness lengths. Systems that include the apparatus and/or perform the operations of the apparatus are also disclosed.

What is claimed is: 
     
         1 . An apparatus for a current pulse supplied with stability compensation, the apparatus comprising:
 a power switch circuit including a high side coupleable to an external device and configured to output current to the external device;   a current sense circuit coupled to the power switch circuit and configured to monitor and limit an amount of the current being output by the power switch circuit; and   a compensation circuit coupled between the current sense circuit and the high side of the power switch circuit, wherein the compensation circuit comprises circuitry to provide gain margin and phase margin over a frequency range that provides stability in the current being output by the power switch circuit over a range of temperatures, input voltages, load impedances, and wiring lengths.   
     
     
         2 . The apparatus of  claim 1 , wherein the circuitry comprises a low pass filter. 
     
     
         3 . The apparatus of  claim 2 , wherein the low pass filter includes a two-pole low pass filter at fifty hertz (50 Hz). 
     
     
         4 . The apparatus of  claim 2 , wherein:
 the current sense circuit comprises a positive-negative-positive (PNP) transistor; and   the low pass filter comprises:
 a first capacitor coupled in series with a first resistor across the PNP transistor, 
 a second capacitor, and 
 a second resistor. 
   
     
     
         5 . The apparatus of  claim 4 , wherein:
 the first capacitor produces a first single pole low pass filter;   the second capacitor produces a second single pole low pass filter;   the first resistor comprises a dampening resistor; and   the second resistor comprises an isolation resistor.   
     
     
         6 . The apparatus of  claim 5 , wherein:
 the dampening resistor is configured to mitigate parasitic current in the apparatus; and   the isolation resistor facilitates creation of the first single pole low pass filter and the second single pole low pass filter.   
     
     
         7 . The apparatus of  claim 6 , wherein:
 the first capacitor comprises a 0.047 μF capacitor;   the second capacitor comprises a 0.047 μF capacitor;   the first resistor comprises a 100Ω resistor; and   the second resistor comprises a 200Ω resistor.   
     
     
         8 . The apparatus of  claim 7 , wherein the first single pole low pass filter and the second single pole low pass filter each roll-off a feedback loop gain of the apparatus at fifty hertz (50 Hz). 
     
     
         9 . A system for a current pulse supplied with stability compensation, the system comprising:
 a pyrotechnic initiator comprising a high side and a low side; and   a current driver comprising:
 a current sense circuit, 
 a power switch circuit coupled to the high side of the pyrotechnic initiator, and 
 a compensation circuit coupled between the current sense circuit and the power switch circuit, wherein the compensation circuit comprises circuitry to provide stability over different current loading conditions to the high side of the pyrotechnic initiator. 
   
     
     
         10 . The system of  claim 9 , wherein the circuitry comprises a low pass filter. 
     
     
         11 . The system of  claim 10 , wherein the low pass filter comprises a two-pole low pass filter at fifty hertz (50 Hz). 
     
     
         12 . The system of  claim 10 , wherein:
 the current sense circuit comprises a positive-negative-positive (PNP) transistor; and   the low pass filter comprises:
 a first capacitor coupled in series with a first resistor across the PNP transistor, 
 a second capacitor, and 
 a second resistor. 
   
     
     
         13 . The system of  claim 12 , wherein:
 the first capacitor produces a first single pole low pass filter;   the second capacitor produces a second single pole low pass filter;   the first resistor comprises a dampening resistor; and   the second resistor comprises an isolation resistor.   
     
     
         14 . The system of  claim 13 , wherein:
 the dampening resistor is configured to mitigate parasitic current in the system; and   the isolation resistor facilitates creation of the first single pole low pass filter and the second single pole low pass filter.   
     
     
         15 . The system of  claim 14 , wherein:
 the first capacitor comprises a 0.047 μF capacitor;   the second capacitor comprises a 0.047 μF capacitor;   the first resistor comprises a 100Ω resistor; and   the second resistor comprises a 200Ω resistor.   
     
     
         16 . The system of  claim 15 , wherein the first single pole low pass filter and the second single pole low pass filter each roll-off a feedback loop gain of the system at fifty hertz (50 Hz). 
     
     
         17 . An aircraft, comprising:
 a control circuit;   a pyrotechnic initiator; and   a current driver coupled between the control circuit and the pyrotechnic initiator, the current driver comprising:
 a current sense circuit, 
 a power switch circuit coupled to the pyrotechnic initiator, and 
 a compensation circuit coupled between the current sense circuit and the power switch circuit, wherein the compensation circuit comprises circuitry to provide stability over different current loading conditions to the pyrotechnic initiator. 
   
     
     
         18 . The aircraft of  claim 17 , wherein:
 the circuitry comprises a low pass filter;   the power switch circuit is coupled to the pyrotechnic initiator via wiring; and   the wiring includes a length of at least thirty meters.   
     
     
         19 . The aircraft of  claim 18 , wherein:
 the low pass filter includes a two-pole low pass filter comprising:
 a first capacitor coupled in series with a first resistor, 
 a second capacitor, and 
 a second resistor; 
   the first capacitor produces a first single pole low pass filter;   the second capacitor produces a second single pole low pass filter;   the first resistor comprises a dampening resistor configured to mitigate parasitic current in the wiring; and   the second resistor comprises an isolation resistor facilitating creation of the first single pole low pass filter and the second single pole low pass filter.   
     
     
         20 . The aircraft of  claim 19 , wherein:
 the first capacitor comprises a 0.047 μF capacitor;   the second capacitor comprises a 0.047 μF capacitor;   the first resistor comprises a 100Ω resistor; and   the second resistor comprises a 200Ω resistor.